Known deposits of tar sands in the United States are large enough to have a major impact on the supply of crude oil. An important consideration with regard to the processing of these tar sands is that most of the deposits of tar sand in the United States are scattered and are not close to the refineries. This fact produces a need for a tar sand refining process and apparatus that can be built as a small module to economically produce on the order of 1,000 to 2,000 barrels per day from these smaller deposits.
Various types of thermal (pyrolysis) processes and solvent extraction processes have heretofore been used to extract synthetic crude from tar sands. Some of the thermal processes presently known involve the use of a variety of horizontal or vertical retort vessels or kilns for the retort. In particular the Lurgi-Rhurgas process uses a mixing screw-type retort and the Tacuik process uses a rotary kiln-type retort. Some of the solvent extraction processes presently known are the Western Tar Sand processes described in the U.S. Pat. Nos. 4,054,505 and 4,054,506 which includes the use of ultrasonic energy, the CAG (Charles-Adams-Garbett) process using a water-base extraction, and the Randall process using hot water. Past practices have generally involved the use of either a thermal process or a solvent extraction process.
Generally, in known solvent extraction processes the tar sand is subjected to a solution in which the bitumen is soluble and in the presence of this solution substantially all of the bitumen is dissolved and the result is a high recovery of the bitumen and a substantially bitumen-free sand product. The advantages in the solvent extraction is the high recovery, a generally lower capital cost, and relative ease in scaling up to larger sizes. The disadvantages of the solvent extraction processes is the expense of solvents, the necessity of shipping solvents to the plant, heat requirements. Further the heavy oil product derived is not suitable for transportation, and difficulty is involved in recovering the solvent from the sand so the sand can be returned to the environment.
The advantages of known thermal processes is that they do not require large amounts of energy, the sand derived is clean and dry, the oil product is transportable and the operating costs are generally low. The disadvantages of known thermal processes are that there is less recovery from the bitumen, the capital costs are higher, the scale-up problems are considerable and there is the problem of handling the waste heat generated.
In U.S. Pat. No. 4,197,183 there is disclosed a combination thermal and solvent extraction process wherein the oil product from the thermal process is fed to the solvent extraction process so that the tar sand undergoes a successive or series heating and then a solvent extraction operation. Heat from the thermal process is disclosed as being used to heat the solvent to maintain the temperature of the solvent extraction operation.